Fix the fw_vboot2 flag not supported in the old devices

Ignore the exception of ChromeOSInterfaceError which happened on the old
devices.

BUG=chrome-os-partner:30387
TEST=None, a quick fix for a broken CL.

Change-Id: I33c38696660f1b3fe8d0b63e1072495102e99e8b
Reviewed-on: https://chromium-review.googlesource.com/207233
Reviewed-by: Daisuke Nojiri <dnojiri@chromium.org>
Tested-by: Wai-Hong Tam <waihong@chromium.org>
Commit-Queue: Wai-Hong Tam <waihong@chromium.org>
diff --git a/client/cros/faft/rpc_functions.py b/client/cros/faft/rpc_functions.py
index fe70001..bef256e 100755
--- a/client/cros/faft/rpc_functions.py
+++ b/client/cros/faft/rpc_functions.py
@@ -261,7 +261,10 @@
 
     def _system_get_fw_vboot2(self):
         """Get fw_vboot2"""
-        return self._chromeos_interface.cs.fw_vboot2 == '1'
+        try:
+            return self._chromeos_interface.cs.fw_vboot2 == '1'
+        except chromeos_interface.ChromeOSInterfaceError:
+            return False
 
     def _system_request_recovery_boot(self):
         """Request running in recovery mode on the restart."""